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View SlideshowRequest to buy this photoEamon Queeney | DISPATCHMary Davis, a research associate at Ohio State University’s Byrd Polar Research Center, holds an ice core from the Quelccaya Ice Cap in Peru.

Twin columns of ancient ice carefully carved from a remote South American glacier are revealing
a year-by-year tropical-climate history over nearly two millennia.

Like rings in a tree trunk, regular layers of ice and dust trapped in the two ice cores offer
the longest and most clearly defined record of annual changes in ocean temperatures and
precipitation in that region of the globe, according to Ohio State University researchers who
brought the cores to Columbus.

These cores promise to help researchers around the world refine the various measuring sticks
they use to track climate change.

“I don’t think we’ll find another site on this planet with that resolution,” OSU climatologist
Lonnie Thompson said by phone from India. “The time scale there is tremendous.”

Thompson and his wife and colleague, Ellen Mosley-Thompson, a distinguished professor of
geography and director of the Byrd Polar Research Center, removed the cores from the Quelccaya Ice
Cap in Peru in 2003.

The Thompsons realized that the Peruvian cores were similar to ice cores they had retrieved from
Tibet and the Himalayas. When they found matches in ice cores taken from opposite sides of Earth,
they knew they had “Rosetta Stones” with which to compare other climate histories from tropical and
subtropical regions. The cores, which show unprecedented detail dating back 1,800 years, will help
link past climate changes around the globe, they said.

Higher concentrations of chlorides found in the Peruvian ice in the 1790s also were found in ice
taken from the Himalayas. They might correspond to widespread monsoon failures reported in Asia
during that period.

“For us, it was very intriguing,” Mosley-Thompson said.

The Quelccaya ice core, which is described in the journal
Science Express, will help climatologists who study historical climate data. “Looking at
ice cores from the tropics has been especially important in allowing us to understand how this very
stable climate system has changed over time,” said Dan-iel Schrag, a Harvard University
climatologist who was not involved in this study.

“Lonnie and Ellen’s tropical ice cores are the definitive pieces of evidence that show us what
we’re seeing today is beyond the scale of any natural cycle,” Schrag said.

The Quelccaya ice is important because it is perched on a wide, flat shelf in a region with
clearly defined wet and dry seasons. Each year’s ice is separated by a thin layer of dust, which is
blown there during dry months.

Researchers can estimate changes in ocean temperature by measuring the ratio of different oxygen
isotopes in frozen water molecules.

The glacier’s flat perch also keeps each layer straight, which makes it easier to compute annual
changes in snowfall, said Ian Howatt, an OSU glaciologist and co-author of the ice-core study.

“That’s the brilliance of what the Thompsons did,” Howatt said. “It was figuring out that you
could get a record from that place, and it would be so good.”